The present invention relates to a distributor-less ignition system for an internal combustion engine, comprising a control unit, an ignition coil coupled to the control unit, the ignition coil having a primary coil switched by the control unit and a secondary coil that has a terminal, and a plurality of spark plugs electrically connected at one end of the secondary coil.
An ignition system of this type if commercially available under the name individual-coil ignition system. The ignition system is associated with each cylinder of the internal combustion engine, this system comprising an ignition coil and the spark plug connected on the secondary side. The ignition coil is preferably located on the cylinder in question. This ignition system has certain problems in various applications regarding weight and mechanical stability. Particularly with internal combustion engines with few cylinders, the mechanical stress brought about by the rough running at spots is considerable.
An object of the invention is to produce an ignition system of the initially-described type which is distinguished by simplified design and simultaneously, low weight.
This and other objects are achieved by the present invention which provides a distributor-less ignition system for an internal combustion engine, comprising a control unit, an ignition coil coupled to the control unit, the ignition coil having a primary coil switched by the control unit and a secondary coil that has a terminal. A plurality of spark plugs are electrically connected at one end of the secondary coil to the same terminal of the secondary coil. A controllable semiconductor switch is respectively electrically connected between the terminal and each of the spark plugs. The semiconductor switch for the spark plug to be triggered is switched at least approximately at the same time by the control unit as the primary coil.
Since several spark plugs are connected in parallel to the ignition coil in certain embodiments of the invention, the weight is reduced. The weight that must additionally be taken into consideration for the semiconductor switch, however, is negligible by comparison. Because of the simultaneous control of both the primary side and the semiconductor switch located in the lead of the spark plug in question, circuitry expenditure is low. On the other hand, by the control of the primary side of the ignition coil and the spark plug in question, i.e. in practice the secondary side of the ignition coil, misfires which occur in an individual-coil ignition system from imperfect control of two primary coils are avoided. Hence the ignition system is controlled on both the primary and secondary sides, making diagnosis particularly easy.
A preferred embodiment of the semiconductor switch is in the form of a thyristor. In general, such a switch can be controlled with particular precision in terms of its switching behavior.
Certain embodiments of the invention in which the semiconductor switch is built into the spark plug connector inserted in the lead to the spark plug have the advantage that they require only a small space for its accommodation. The arrangement of the thyristor inside the spark plug connector is easily possible.
Making the semiconductor switch an optically triggerable switch in certain embodiments of the invention provides electrical insulation. The lead to the semiconductor switch can be in the form of a light guide and is hence particularly low in weight and free of insulation problems.
Certain embodiments of the invention have advantageous design features which are distinguished by low volume. In this regard U.S. Pat. No. 5,109,829 teaches a distributor-less ignition system with a high-voltage switch. The semiconductor components are disposed on the bottom of a cone at whose vertex the light-emitting element is located. The cone is formed within a housing which is provided with filler material outside the cone. This results in expensive construction and relatively high weight. Moreover, if a large number of semi,conductor components are to be triggered optically, it is necessary to provide a corresponding number of light-emitting elements, which has a negative impact on cost, weight, and the space required to accommodate the switch.
By arranging the semiconductor components around the light-emitting element, as provided in certain embodiments, the number of semiconductor components to be triggered optically by the light-emitted element does not depend on the distance from it but on the size of the surface area of the light-emitting element. Instead of an LED as with the known high-voltage switch, a xenon tube is suitable for this purpose. It has a high light intensity with good triggering behavior and is, simple and sturdy to build and handle.
Features of certain embodiment of the present invention provide the possibility of connecting the spark plugs in a cylinder-selective manner to the high voltage, starting from one spark coil and using spark plug connectors of this type. The additional space required per spark plug is relatively small and looks externally like a mere axial extension of the spark plug connector.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.